1. Field of the Invention
The invention generally relates to a position detecting apparatus for an actuator, and a variable valve lift mechanism for an internal combustion engine, which includes the position detecting apparatus. More particularly, the invention relates to a position detecting apparatus for an actuator which converts rotational movement to linear movement and outputs the linear movement, and a variable valve lift mechanism for an internal combustion engine, which includes the position detecting apparatus.
2. Description of the Related Art
With regard to a position detecting apparatus for an actuator, for example, Japanese Patent Application Publication No. JP (A) 2004-48875 discloses an abnormality detecting apparatus for a motor drive system, which can detect an abnormality of a sensor with a simple configuration. The motor drive system disclosed in the Japanese Patent Application Publication No. JP (A) 2004-48875 includes a drive shaft which is connected to an output shaft of a motor through plural gears and ball screws, and which is linearly moved in response to rotation of the output shaft. In the motor drive system, a displacement amount sensor which detects a displacement amount in an axial direction of the drive shaft is provided.
Also, Japanese Patent Application Publication No. JP (A) 2002-213219 discloses a variable valve drive apparatus for an internal combustion engine, which is configured so as to increase a life span of an electric motor. Further, Japanese Patent Application Publication No. JP (A) 2002-206423 discloses an intake air control apparatus for an internal combustion engine, which is configured so as to suppress an increase in a temperature of an electric motor, and to maintain response at a high level in control of an intake air amount.
In the abnormality detecting apparatus for a motor drive system disclosed in the Japanese Patent Application Publication No. JP (A) 2004-48875, an actual displacement amount of the drive shaft detected by the displacement amount sensor is compared to a target displacement amount of the drive shaft calculated by an electronic control unit for an engine, and feedback control of the displacement amount of the drive shaft is performed so that the actual displacement amount becomes equal to the target displacement amount.
However, when such a displacement amount sensor is used for controlling the motor drive system, it is necessary to newly provide a component that is exclusively used for the sensor, such as a component whose position is detected by the sensor. Accordingly, the number of components increases, and production cost of the apparatus increases.